This invention relatesgenerally to telemetry systems for physiological implants and more particularly, it relates to a telemetry system for transmitting internal signals from an implanted cardiac pacer to an external programming/receiver unit which utilizes a pulse generator having an output period proportional to its input voltage magnitude.
In the field of implanted cardiac pacers, there has been developed in the prior art a variety of telemetry systems for signalling out data from the implented pacer. However, many of these prior art systems relied on the use of telemetered data which was based upon analog information transmission. As a result, these prior art telemetry systems encountered the problem of distortion in the recovery of the telemetered analog data from the pacer as the distance between the pacer and the external receiver unit changed. Another problem associated with implanted pacers is the lacking of information relating to conditions of the pacer such as the remaining life of the battery, the pulse voltage and the pulse current.
It would therefore be desirable to provide an improved telemetry system for transmitting digital data from an implanted pacer so as to avoid the problem of distortion. The telemetry system of the present invention utilizes a pulse generator having an output period proportional to its input voltage magnitude. The telemetered digital data corresponding to conditions of the pacer may be recovered in an external programming/receiver unit by a pulse period detector which generates an analog signal whose magnitude is proportional to each pulse period from the pulse generator.